The present invention relates in general to electronic control systems for fuel injection of a diesel engine, the system including sensors for detecting operational variables which determine operational condition of the engine, a set of characteristics for a smoke discharge limiter, means for interpreting the set of characteristics in dependency at least on rotary speed of the engine to produce a signal indicative of mass of fuel supplied to the engine, means for generating in dependency on rotary speed a simulation signal indicative of air mass supplied to the engine, and means for evaluating the sensed operational variables to determine operative condition of the engine.
It is known from prior art to detect by means of sensors in a charged diesel engine the charging air temperature and charging air pressure and to apply the detected values for controlling the quantity of fuel supplied to the engine. Known is also from German Patent application No. P 32 04 804.1 a smoke discharge limiter which in order to determine operational variables of the engine does not need any sensors. In using the two mode operations in connection with a charged diesel engine, however, it is not possible to guarantee a satisfactory operation of each system, for example, in the case of the failure of the sensor for charging air pressure.